Speed.
That is just one of the things that the themarians have that are above almost every other race except the evaniels. And explosive speed is something that James seems to excel at.
The fact that he was able to move away before getting hit by Riley's pavoom move was already enough of a display of that. But now, even Zac was not able to see what just happened.
"..." He looked at the thing that was hanging on James's hand, and then above Riley's shoulders. And true enough, things that should not be where they are, are.
James then started moving the clump of long white hair in his hand, causing Riley's decapitated head to swing like a pendulum. And soon, at the 3rd second, the rest of Riley's body fell to the floor.
"You're Star Sergeant Zac, correct?" James did not immediately walk up the stairs, and instead even turned around to talk to Zac, causing Riley's head to swing even more wildly.
